Atomic layer deposition apparatus and method

ABSTRACT

An atomic layer deposition method includes positioning a semiconductor substrate within an atomic layer deposition chamber. A first deposition precursor is fed to the chamber under first vacuum conditions effective to form a first monolayer on the substrate. The first vacuum conditions are maintained at least in part by a first non-roughing vacuum pump connected to the chamber and through which at least some of the first deposition precursor flows. After forming the first monolayer, a purge gas is fed to the chamber under second vacuum conditions maintained at least in part by a second non-roughing vacuum pump connected to the chamber which is different from the first non-roughing vacuum pump and through which at least some of the purge gas flows. An atomic layer deposition apparatus is disclosed.

RELATED PATENT DATA

This patent resulted from a continuation application of U.S. patentapplication Ser. No. 11/055,487, filed Feb. 11, 2005 now U.S. Pat. No.7,030,037, entitled “Atomic Layer Deposition Apparatus and Method”,naming Trung Tri Doan and Gurtej S. Sandhu as inventors, the disclosureof which is incorporated by reference; which resulted from acontinuation application of U.S. patent application Ser. No. 10/741,300,filed Dec. 17, 2003, entitled “Atomic Layer Deposition Apparatus andMethod”, naming Trung Tri Doan and Gurtej S. Sandhu as inventors, nowabandoned, the disclosure of which is incorporated by reference; whichresulted from a divisional application of U.S. patent application Ser.No. 10/097,025, filed Mar. 11, 2002, entitled “Atomic Layer DepositionApparatus and Method”, naming Trung Tri Doan and Gurtej S. Sandhu asinventors, now U.S. Pat. No. 6,893,506 B2, the disclosure of which isincorporated by reference.

TECHNICAL FIELD

This invention relates to atomic layer deposition.

BACKGROUND OF THE INVENTION

Atomic layer deposition involves the deposition of successive monolayersover a substrate within a deposition chamber typically maintained atsubatmospheric pressure. An exemplary such method includes feeding asingle vaporized precursor to a deposition chamber effective to form afirst monolayer over a substrate received therein. Thereafter, the flowof the first deposition precursor is ceased and an inert purge gas isflowed through the chamber effective to remove any remaining firstprecursor which is not adhering to the substrate from the chamber.Subsequently, a second vapor precursor different from the first isflowed to the chamber effective to form a second monolayer on/with thefirst monolayer. The second monolayer might react with the firstmonolayer. Additional precursors can form successive monolayers, or theabove process can be repeated until a desired thickness and compositionlayer has been formed over the substrate.

The invention includes improvements in apparatus and methods of atomiclayer depositions, whether existing or yet-to-be developed, whereby atleast one monolayer is formed over a substrate.

SUMMARY

The invention includes atomic layer deposition methods and apparatus. Inone implementation, an atomic layer deposition method includespositioning a semiconductor substrate within an atomic layer depositionchamber. A first deposition precursor is fed to the chamber under firstvacuum conditions effective to form a first monolayer on the substrate.The first vacuum conditions are maintained at least in part by a firstnon-roughing vacuum pump connected to the chamber and through which atleast some of the first deposition precursor flows. After forming thefirst monolayer, a purge gas is fed to the chamber under second vacuumconditions maintained at least in part by a second non-roughing vacuumpump connected to the chamber which is different from the firstnon-roughing vacuum pump and through which at least some of the purgegas flows.

In one implementation, an atomic layer deposition apparatus includes anatomic layer deposition chamber having a substrate passagewaycommunicating to externally of the chamber. A first non-roughing vacuumpump is in fluid communication with the chamber apart from the substratepassageway. A second non-roughing vacuum pump is in fluid communicationwith the chamber apart from the substrate passageway.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic depiction of an atomic layer depositionapparatus in accordance with an aspect of the invention.

FIG. 2 is a diagrammatic depiction of an atomic layer depositionapparatus in accordance with an aspect of the invention.

FIG. 3 is a diagrammatic depiction of an atomic layer depositionapparatus in accordance with an aspect of the invention.

FIG. 4 is a sectional view taken through line 4-4 in FIG. 3.

FIG. 5 is an alternate embodiment sectional view as would be takenthrough line 4-4 in FIG. 3.

FIG. 6 is a diagrammatic depiction of an atomic layer depositionapparatus in accordance with an aspect of the invention in a firstoperational state.

FIG. 7 is a view of the FIG. 6 apparatus in a second operational state.

FIG. 8 is a diagrammatic depiction of an atomic layer depositionapparatus in accordance with an aspect of the invention.

FIG. 9 is a diagrammatic depiction of an atomic layer depositionapparatus in accordance with an aspect of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

FIG. 1 depicts a first embodiment atomic layer deposition apparatus 10.Such comprises an atomic layer deposition chamber 12 having a substratepassageway 14 communicating to externally of the chamber. A load chamber16 is in fluid communication with atomic layer deposition chamber 12through substrate passageway 14. A load chamber vacuum pump isdiagrammatically depicted with numeral 18, and is in fluid communicationwith load chamber 16 apart from through substrate passageway 14. Loadchamber vacuum pump 18 includes an illustrated discharge indicated by adownward arrow, and a by-pass inlet illustrated by a horizontal arrowpointing to the left proximate thereto. In the preferred embodiment,additional vacuum pumps might be associated with load chamber 16 and/orpump 18 could be configured to include a roughing vacuum pump apparatusand a non-roughing vacuum pump apparatus. In the context of thisdocument, a “roughing vacuum pump” is a vacuum pump (or sub-pumpingcomponents/apparatus of a non-roughing vacuum pump) which is configuredto provide an initial reduced pressure from at or near atmosphericpressure, and which is used with a non-roughing vacuum pump that furtherreduces pressure. Also in the context of this document, a “non-roughingvacuum pump” is a vacuum pump configured to provide a subatmosphericdeposition operating pressure within the chamber.

In the illustrated exemplary embodiment, atomic layer deposition chamber12 is provided with three gas inlets 20, 22 and 24. By way of exampleonly, any two of such inlets might be configured for feeding differentdeposition precursors to chamber 12, with the remaining inlet beingconfigured for feeding a purge gas to deposition chamber 12.

A first non-roughing vacuum pump 26 is in fluid communication withdeposition chamber 12 apart from substrate passageway 14. A secondnon-roughing vacuum pump 28 is in fluid communication with depositionchamber 12 apart from substrate passageway 14. Any suitable pumpscapable of producing a desired subatmospheric deposition pressure arecontemplated whether existing or yet-to-be developed. By way of exampleonly, such include turbomolecular pumps, diffusion pumps, sublimationpumps, cryo pumps, diffusion ejector pumps, absorption pumps,sliding-vane rotary pumps, rotary piston pumps, rotary plunger pumps,root pumps, etc. A roughing vacuum pump 30 is provided in fluidcommunication with chamber 12 apart from substrate passageway 14. Asdescribed above with respect to load chamber vacuum pump 18, a roughingvacuum pump may or may not be utilized, and might alternately comprise asub-pumping device of non-roughing vacuum pump assemblies. Further, suchmight be in fluid communication with chamber 12 through a separate linefrom non-roughing vacuum pumps 26 and 28 (as shown), or through conduitsor other gas passageways (not shown) associated with non-roughing vacuumpumps 26 and 28. Further of course, non-roughing vacuum pumps 26 and 28could comprise respective multiple pumping devices/components/apparatus(roughing and/or non-roughing) connected in series and/or in parallel.

The first and second non-roughing vacuum pumps can be configured to havedifferent rated throughputs over a given operating pressure range.Alternately, the first and second non-roughing vacuum pumps can beconfigured to have common rated throughputs over a given operatingpressure range. Second non-roughing vacuum pump 28 is depicted as beingdiagrammatically larger than first non-roughing vacuum pump 26, therebyhaving corresponding larger and smaller throughputs, respectively. Insuch depicted preferred embodiment, second non-roughing vacuum pump 28is configured with chamber 12 for feeding a purge gas to the chamber,while first non-roughing vacuum pump 26 is configured with chamber 12for feeding a deposition precursor to the chamber. For example, and byway of example only, it might be desirable to draw or feed the purge gasthrough the system at much higher throughput over a given pressure rangethan a throughput which would be desired over a given pressure range(under the same or different pressure range) for a deposition precursor.Also, first and second non-roughing vacuum pumps 26 and 28 might beconfigured for operating at variable speeds over a given operatingpressure range, or configured for operating at respective constantspeeds over a given operating pressure range. Further, one may beconfigured for operating at a constant speed over a given operatingpressure range with the other being configured for operating at variablespeeds over a given operating pressure range.

FIG. 1 depicts an embodiment whereby chamber 12 is provided withmultiple outlets 32 and 34, with one of said outlets (outlet 32) beingin fluid communication with first non-roughing vacuum pump 26 andanother of said outlets (outlet 34) being in fluid communication withsecond non-roughing vacuum pump 28. Of course, pressure control valvingor other apparatus could be associated with one or more of theillustrated pumps, outlets and/or conduits for controlling the pressure,or isolating one or more pumps from the chamber while one or more otherpump(s) operate(s) relative to the chamber. For example, by-pass inletsare illustrated by respective horizontal arrows pointing to the rightproximate each pump, for example should a pump be isolated fromcommunicating with chamber 12 during operation. Such might be used tominimize transient pressure changes with respect to the feedlines whenswitching between pumps.

FIG. 2 illustrates an alternate embodiment 10 a. Like numerals from thefirst embodiment are utilized where appropriate, with differences beingindicated by the suffix “a” or with different numerals. Atomic layerdeposition apparatus 10 a is provided with one outlet 38 at chamber 12which is in fluid communication with both first and second non-roughingvacuum pumps 26 a and 28 a, respectively. In this exemplary depictedpreferred embodiment, a suitable conduit 40 extends from outlet 38.First and second non-roughing vacuum pumps 26 a and 28 a, respectively,are in fluid communication with conduit 40. At least one isolation valveis associated with the illustrated first and second pumps. In thedepicted preferred embodiment, there is one and only one such isolationvalve diagrammatically depicted as an embodiment 42. Further in thedepicted embodiment, isolation valve assembly 42 is in the form of apivotable flap valve 44 received within conduit 40 and configured forselectively isolating the first and second pumps 26 a and 28 a,respectively, from fluid communication with conduit 40.

FIGS. 3-5 depict an alternate embodiment atomic layer depositionapparatus 10 b. Like numerals from the first and second describedembodiments are utilized where appropriate, with differences beingindicated by the suffix “b” or with different numerals. Atomic layerdeposition apparatus 10 b includes a rotatable valve 42 b receivedwithin conduit 40 b, and which is configured for selectively isolatingfirst and second pumps 26 b and 28 b, respectively, from fluidcommunication with conduit 40 b. Rotatable valve 42 b is depicted in theexemplary embodiment as being mounted for rotation about a central axis43. A valve opening 46 is received radially from axis 43 and can beselectively positioned to provide flow relative to second non-roughingvacuum pump 28 b (as shown), or with respect to first non-roughingvacuum pump 26 b by 180° rotation about axis 43 (not shown).

FIG. 5 depicts an exemplary alternate embodiment rotatable valve 48having two adjacent valve openings 50 and 52 positioned proximate to butradially 90° from one another. This particular exemplary embodimentwould enable switching between first non-roughing vacuum pump 26 b andsecond non-roughing vacuum pump 28 b by 90° rotation as opposed to the180° of rotation with respect to the 42 b diagrammatic embodiment.

FIGS. 6 and 7 illustrate another alternate embodiment atomic layerdeposition apparatus 10 c, and in different respective operationalconfigurations. Like numerals from the above-described embodiments areutilized where appropriate, with differences being indicated with thesuffix “c”, or with different numerals. Valve assembly 42 c is depicteddiagrammatically as a slidable valve received within conduit 40 c andconfigured for selectively isolating first and second pumps 26 c and 28c, respectively, from fluid communication with conduit 40 c. FIG. 6depicts one operational configuration where valve 42 c is slid toprovide fluid communication of pump 26 c with conduit 40 c, while secondpump 28 c is restricted from fluid communication with conduit 40 c. FIG.7 depicts the opposite.

Of course, any additional or alternate isolating valving assemblies,whether existing or yet-to-be developed, might be utilized.

FIG. 8 illustrates another alternate embodiment atomic layer depositionapparatus 10 d. Like numerals from the above-described embodiments areutilized where appropriate, with differences being indicated with thesuffix “d”, or with different numerals. Atomic layer depositionapparatus 10 d comprises a third non-roughing vacuum pump 60 d in fluidcommunication with chamber 12 d apart from substrate passageway 14. Inone preferred embodiment, third non-roughing vacuum pump 60 d isconfigured with chamber 12 d for feeding a second deposition precursorto chamber 12 d. For example, in one preferred embodiment, separateprecursor feed pumps (i.e., pumps 26 d and 60 d) are separatelyoptimized for their respective different deposition precursors (forexample, in one or both of materials of construction or designedthroughput) while another of the non-roughing vacuum pumps (i.e., pump28 d) is configured for feeding a purge gas to the chamber (for example,with respect to desired higher throughput than with the depositionprecursors).

The FIG. 8 depicted embodiment shows chamber 12 d as being provided withmultiple outlets 32 d, 34 d and 62 d, which are in respective fluidcommunication with first non-roughing vacuum pump 26 d, secondnon-roughing vacuum pump 28 d and third non-roughing vacuum pump 60 d,respectively. FIG. 9 depicts an alternate embodiment atomic layerdeposition apparatus 10 e wherein a chamber 12 e is provided with oneoutlet 40 e at the chamber. Outlet 40 e is in fluid communication witheach of first, second and third non-roughing vacuum pumps 32 e, 34 e and60 e, respectively. Of course, more than three non-roughing vacuum pumpscould be utilized.

The invention contemplates an atomic layer deposition method using theabove-described apparatus, and methods independent thereof. In otherwords, the concluding apparatus claims are not limited by the methodclaims, nor are the concluding method claims limited by any attribute ofthe apparatus claims, unless literal language appears in such claims andwithout any limiting or interpretative reference to the specification ordrawings. The respective method claim families and apparatus claimfamilies stand as literally worded without reference to the other. Anexemplary first embodiment atomic layer deposition method in accordancewith the invention positions a semiconductor substrate within an atomiclayer deposition chamber, for example any of the above-describedchambers. In the context of this document, the term “semiconductorsubstrate” or “semiconductive substrate” is defined to mean anyconstruction comprising semiconductive material, including, but notlimited to, bulk semiconductive materials such as a semiconductive wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure, including, but not limited to, the semiconductive substratesdescribed above. Such positioning can occur by passing a substrate 70 tobe processed from load chamber 16 through substrate passageway 14 onto asuitable substrate holder (not shown) within atomic layer depositionchamber 12. A first deposition precursor is fed through the chamberunder first vacuum conditions effective to form a first monolayer on thesubstrate. The first vacuum conditions are maintained, at least in part,by a first non-roughing vacuum pump connected to the chamber and throughwhich at least some of the first deposition precursor flows.

After forming the first monolayer, a purge gas is fed to the chamberunder second vacuum conditions maintained, at least in part, by a secondnon-roughing vacuum pump connected to the chamber, which is differentfrom the first non-roughing vacuum pump, and through which at least someof the purge gas flows. In one preferred embodiment, a roughing vacuumpump is utilized to lower chamber pressure prior to feeding the firstdeposition precursor. In one preferred embodiment, after feeding thepurge gas, a second deposition precursor, different from the firstdeposition precursor, is fed to the chamber effective to form a secondmonolayer on the first monolayer. In the context of atomic layerdeposition, any existing or yet-to-be developed deposition precursorsare of course contemplated. The second deposition precursor feedingmight be conducted under third vacuum conditions effective to form asecond monolayer on the first monolayer using the first non-roughingvacuum pump. Alternately by way of example only, the second depositionprecursor feeding to the chamber might be conducted under third vacuumconditions maintained, at least in part, by a third non-roughing vacuumpump connected to the chamber, which is different from the first andsecond non-roughing vacuum pumps.

In one preferred embodiment, the first vacuum conditions include asubstantially constant vacuum pressure within the chamber. In anotherpreferred embodiment, the first vacuum conditions include varied vacuumpressure within the chamber. In yet another preferred embodiment, thevacuum pressure within the chamber is substantially the same under thefirst and second vacuum conditions, and in a most preferred embodiment,the vacuum pressure is substantially constant within the chamber underthe first and second vacuum conditions. In another preferred embodiment,the vacuum pressure within the chamber is different under the first andsecond vacuum conditions, and in a sub-embodiment, preferably is bothsubstantially constant during each of the first and second vacuumconditions but different from one another under the first and secondvacuum conditions.

In one preferred embodiment, an atomic layer deposition method inaccordance with the invention includes isolating the first non-roughingvacuum pump from the chamber during at least some of the purge gasfeeding. In another preferred embodiment, the method includes isolatingthe second non-roughing vacuum pump from the chamber during at leastsome of the first deposition precursor feeding, and in onesub-embodiment, preferably during all of the first deposition precursorfeeding.

In one preferred embodiment, the method comprises operating the secondnon-roughing vacuum pump at a higher pumping speed during the purge gasfeeding than the first non-roughing vacuum pump is operated at duringthe first deposition precursor feeding.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A deposition apparatus, comprising: a deposition chamber adapted fordepositing monolayers and which is sized to retain no more than a singlewafer at a time for depositing of monolayers upon, the depositionchamber having a substrate passageway communicating to externally of thedeposition chamber; a first non-roughing vacuum pump in fluidcommunication with the deposition chamber apart from the substratepassageway; a second non-roughing vacuum pump in fluid communicationwith the deposition chamber apart from the substrate passageway; and aroughing vacuum pump in fluid communication with the deposition chamberapart from the substrate passageway and through a conduit separate fromwhich the first and second non-roughing vacuum pumps are in fluidcommunication with the deposition chamber.
 2. The apparatus of claim 1comprising a third non-roughing vacuum pump in fluid communication withthe deposition chamber apart from the substrate passageway.
 3. Theapparatus of claim 1 comprising a load chamber in fluid communicationwith the deposition chamber through the substrate passageway, and a loadchamber vacuum pump in fluid communication with the load chamber apartfrom the substrate passageway.
 4. The apparatus of claim 1 wherein thefirst non-roughing vacuum pump is configured for feeding a depositionprecursor to the deposition chamber and the second non-roughing vacuumpump is configured for feeding a purge gas to the deposition chamber. 5.The apparatus of claim 1 wherein the first and second non-roughingvacuum pumps are configured for operating at variable speeds over agiven operating pressure range.
 6. The apparatus of claim 1 wherein thefirst and second non-roughing vacuum pumps are configured for operatingat respective constant speeds over a given operating pressure range. 7.The apparatus of claim 1 wherein one of the first and secondnon-roughing vacuum pumps is configured for operating at a constantspeed over a given operating pressure range, and the other of the firstand second non-roughing vacuum pumps is configured for operating atvariable speeds over a given operating pressure range.
 8. The apparatusof claim 1 wherein the deposition chamber is provided with multipleoutlets at the deposition chamber, one of said outlets being in fluidcommunication with the first non-roughing vacuum pump, another of saidoutlets being in fluid communication with the second non-roughing vacuumpump.
 9. The apparatus of claim 1 wherein the deposition chamber isprovided with one outlet at the deposition chamber which is indownstream fluid communication with both the first and secondnon-roughing vacuum pumps.
 10. The apparatus of claim 9 comprising: aconduit extending from the one outlet, the first and second non-roughingvacuum pumps being in fluid communication with the conduit; and at leastone first pump and second pump isolation valve.
 11. The apparatus ofclaim 9 comprising: a conduit extending from the one outlet, the firstand second non-roughing vacuum pumps being in fluid communication withthe conduit; and one and only one first pump and second pump isolationvalve.
 12. The apparatus of claim 9 comprising: a conduit extending fromthe one outlet, the first and second non-roughing vacuum pumps being influid communication with the conduit; and a pivotable flap valvereceived within the conduit configured for selectively isolating thefirst and second pumps from fluid communication with the conduit.
 13. Adeposition apparatus, comprising: a deposition chamber adapted fordepositing monolayers and which is sized to retain no more than a singlewafer at a time for depositing monolayers upon, the deposition chamberhaving a substrate passageway communicating to externally of thedeposition chamber; a first non-roughing vacuum pump in fluidcommunication with the deposition chamber apart from the substratepassageway; a second non-roughing vacuum pump in fluid communicationwith the deposition chamber apart from the substrate passageway; thedeposition chamber being provided with one outlet at the depositionchamber which is in downstream fluid communication with both the firstand second non-roughing vacuum pumps; a conduit extending from the oneoutlet, the first and second non- roughing vacuum pumps being in fluidcommunication with the conduit; and a rotatable valve plate receivedwithin the conduit configured for selectively isolating the first andsecond pumps from fluid communication with the conduit, the rotatablevalve plate being rotatable about an axis of rotation which is parallelwith a line of gas flow path through the rotatable valve plate.
 14. Adeposition apparatus, comprising: a deposition chamber adapted fordepositing monolayers and which is sized to retain no more than a singlewafer at a time for depositing upon, the deposition chamber having asubstrate passageway communicating to externally of the depositionchamber; a first non-roughing vacuum pump in fluid communication withthe deposition chamber apart from the substrate passageway, the firstnon-roughing vacuum pump being configured with the deposition chamberfor feeding a first deposition precursor to the deposition chamber; asecond non-roughing vacuum pump in fluid communication with thedeposition chamber apart from the substrate passageway, the secondnon-roughing vacuum pump being configured with the deposition chamberfor feeding a purge gas to the deposition chamber; a third non-roughingvacuum pump in fluid communication with the deposition chamber apartfrom the substrate passageway, the third non-roughing vacuum pump beingconfigured with the deposition chamber for feeding a second depositionprecursor to the deposition chamber; and a roughing vacuum pump in fluidcommunication with the deposition chamber apart from the substratepassageway and through a conduit separate from which the first andsecond non-roughing vacuum pumps are in fluid communication with thedeposition chamber.
 15. The apparatus of claim 14 comprising a loadchamber in fluid communication with the deposition chamber through thesubstrate passageway, and a load chamber vacuum pump in fluidcommunication with the load chamber apart from the substrate passageway.16. The apparatus of claim 14 wherein the first and third non-roughingvacuum pumps have different rated maximum throughput capacities over agiven operating pressure range as compared to the second non-roughingvacuum pump.
 17. The apparatus of claim 16 wherein the secondnon-roughing vacuum pump has a higher rated maximum throughput capacitythan either of the first and second non-roughing vacuum pumps.
 18. Theapparatus of claim 14 wherein the deposition chamber is provided withmultiple outlets at the deposition chamber, one of said outlets being influid communication with the first non-roughing vacuum pump, another ofsaid outlets being in fluid communication with the second non-roughingvacuum pump, still another of said outlets being in fluid communicationwith the third non-roughing vacuum pump.
 19. The apparatus of claim 14wherein the deposition chamber is provided with one outlet at thedeposition chamber which is in downstream fluid communication with eachof the first, second and third non-roughing vacuum pumps.
 20. Adeposition apparatus, comprising: a deposition chamber adapted fordepositing monolayers and which is sized to retain no more than a singlewafer at a time for depositing monolayers upon, the deposition chamberhaving a substrate passageway communicating to externally of thedeposition chamber; a first non-roughing vacuum pump in fluidcommunication with the deposition chamber apart from the substratepassageway; a second non-roughing vacuum pump in fluid communicationwith the deposition chamber apart from the substrate passageway; thedeposition chamber being provided with one outlet at the depositionchamber which is in downstream fluid communication with both the firstand second non-roughing vacuum pumps; a conduit extending from the oneoutlet, the first and second non-roughing vacuum pumps being in fluidcommunication with the conduit; and a rotatable valve plate receivedwithin the conduit configured for selectively isolating the first andsecond pumps from fluid communication with the conduit, the rotatablevalve plate being rotatable about an axis of rotation which is parallelwith a line of gas flow path through the rotatable valve plate, therotatable valve plate being configured for rotation about a minimum of180° in switching between isolating the first and second pumps from oneanother relative to the conduit.
 21. A deposition apparatus, comprising:a deposition chamber adapted for depositing monolayers and which issized to retain no more than a single wafer at a time for depositingmonolayers upon, the deposition chamber having a substrate passagewaycommunicating to externally of the deposition chamber; a firstnon-roughing vacuum pump in fluid communication with the depositionchamber apart from the substrate passageway; a second non-roughingvacuum pump in fluid communication with the deposition chamber apartfrom the substrate passageway; the deposition chamber being providedwith one outlet at the deposition chamber which is in downstream fluidcommunication with both the first and second non-roughing vacuum pumps;a conduit extending from the one outlet, the first and secondnon-roughing vacuum pumps being in fluid communication with the conduit;and a rotatable valve plate received within the conduit configured forselectively isolating the first and second pumps from fluidcommunication with the conduit, the rotatable valve plate beingrotatable about an axis of rotation which is parallel with a line of gasflow path through the rotatable valve plate, the rotatable valve platebeing configured for rotation about a minimum of 90° in switchingbetween isolating the first and second pumps from one another relativeto the conduit.